(1) Field of the Invention
The present invention relates to an apparatus and method of use for determining the shear strength of a composite sandwich beam using measurable hydrostatic loads.
(2) Description of the Prior Art
A composite sandwich is a load bearing structure that typically has thin but stiff face sheets and a lightweight but soft core. This type of structure offers an excellent strength to weight ratio. For this reason, composite sandwiches are increasingly considered for use in naval structures such as boat hulls and pressure vessels (i.e., launch canisters and torpedo tubes).
When a composite sandwich is loaded with a force normal to the face sheet, the core is loaded in shear. Failure of the core in shear is a prevalent failure mode of composite sandwiches.
The historical method of testing the shear strength of a composite sandwich is to test a composite beam in a three or four point bend. The three or four point bend test method creates stress concentrations under the loading points. These stress concentrations would not be located in a real world situation when a sandwich panel would be loaded under a hydrostatic load. Also, the stress concentrations can cause premature failure of the composite sandwich panel. This failure is particularly true in cases where the core material is brittle or very soft.
As such, a need exists for loading over the face or faces of a composite sandwich panel or beam such that stress concentrations of loading can be eliminated or reduced when a shear strength test is conducted on the composite sandwich beam.